Magnetic materials used for various transformers, reactor choke coils, noise-reducing parts, pulse power magnetic parts for laser power sources and accelerators, motors, generators, etc. are silicon steel, ferrite, Co-based amorphous alloys, Fe-based, amorphous alloys, Fe-based, nano-crystalline alloys, etc., because they need high saturation magnetic flux density and excellent AC magnetic properties.
Silicon steel plates that are inexpensive and have a high magnetic flux density are extremely difficult to be made as thin as amorphous ribbons, and suffer large core loss at high frequencies because of large eddy current loss. Ferrite is unsuitably magnetically saturated in high-power applications needing a large operation magnetic flux density, because it has a small saturation magnetic flux density. The Co-based amorphous alloys have as low saturation magnetic flux density as 1 T or less, thereby making high-power parts large. Their core loss increases with time because of thermal instability. Further, they are costly because Co is expensive.
As the Fe-based, amorphous alloy, JP 5-140703 A discloses an Fe-based, amorphous alloy ribbon for a transformer core having a composition represented by (FeaSibBcCd)100-xSnX (atomic %), wherein a is 0.80-0.86, b is 0.01-0.12, c is 0.06-0.16, d is 0.001-0.04, a+b+c+d=1, and x is 0.05-1.0, the alloy ribbon having excellent soft magnetic properties, such as good squareness, low coercivity, and large magnetic flux density. However, this Fe-based, amorphous alloy has a low saturation magnetic flux density, because the theoretical upper limit of the saturation magnetic flux density determined by interatomic distance, the number of coordination and the concentration of Fe is as low as about 1.65 T. It also has such large magnetostriction that its properties are easily deteriorated by stress. It further has a low S/N ratio in an audible frequency range. To increase the saturation magnetic flux density of the Fe-based, amorphous alloy, proposal has been made to substitute part of Fe with Co, Ni, etc., but its effect is insufficient despite high cost.
As the Fe-based, nano-crystalline alloy, JP 1-156451 A discloses a soft-magnetic, Fe-based, nano-crystalline alloy having a composition represented by (Fe1-aCoa)100-x-y-z-αCuxSiyBzM′α (atomic %), wherein M′ is at least one element selected from the group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo, and a, x, y, z and α are numbers meeting the conditions of 0≦a≦0.3, 0.1≦x≦3, 3≦y≦6, 4≦z≦17, 10≦y+z≦20, and 0.1≦α≦5, 50% or more of the alloy structure being occupied by crystal grains having an average diameter of 1000 angstrom or less. However, this Fe-based, nano-crystalline alloy has an unsatisfactory saturation magnetic flux density of about 1.5 T.
JP 2006-40906 A discloses a method for producing a soft magnetic ribbon comprising the steps of quenching an Fe-based alloy melt to form a 180°-bendable ribbon having a mixed phase structure, in which an α-Fe crystal phase having an average diameter of 50 nm or less is dispersed in an amorphous phase, and heating the ribbon to a temperature higher than the crystallization temperature of the α-Fe crystal phase. However, this soft magnetic ribbon has an unsatisfactory saturation magnetic flux density of about 1.6 T.